Embodiments of the present invention relate to a semiconductor memory device including a security function.
A semiconductor memory device has been rapidly developed to temporarily or permanently store data therein. The semiconductor memory device has been widely used in a variety of electronic appliances, electronic devices, and personal portable devices. General semiconductor memory devices can freely read and/or write data, and can also easily replace old data with new data. However, regarding important information, the forgery or modification of this information needs to be prevented. When important data is recorded in a semiconductor memory device, an improved function for preventing the forgery or modification of such important information needs to be developed.
In compliance with the demand of developing the improved function, a one time programmable (OTP) function (hereinafter referred to as an OTP device) is added to the semiconductor memory device. The OTP device is needed for implementing the security. Some semiconductor memory devices use lock-status unit cells to prevent important or significant data from overlapping, such that it is impossible to implement a write or program function on the lock-status unit cells.
For example, some of the non-volatile semiconductor memory devices provide some parts of a unit-cell array as an OTP array. A cell array including a controller for preventing a lock-status unit cell from being returned to an unlock status is called an OTP array. The OTP array stores important data including security data such as a serial number, manufacturer's information, date when the semiconductor memory device was manufactured and the like. Therefore, the data once-programmed in the OTP array needs to be safely protected from external manipulation, and not be modified or changed by a subsequent programming operation.